Snake sperm structure: the influence of sperm competition and reproductive mode

TOURMENTE, MAXIMILIANO; GOMENDIO, MONTSERRAT; ROLDAN, EDUARDO R. S.; GIOJALAS, LAURA C.; CHIARAVIGLIO, MARGARITA

Sheffield

Congreso; 9th Biology of Spermatozoa Meeting; 2007

University of Sheffield

Due to their variability in reproductive modes and mating systems, snakes are excellent models for SC. In order to evidence the influence of SC over sperm dimensions, we compared sperm morphometry among 19 snake species. We also examined the ultrastructure of the midpiece of 4 species with different reproductive modes and levels of sperm competition. Sperm competition has a strong effect upon midpiece length and a weaker effect upon principal piece length after controlling for phylogenetic effects.The midpiece is the longer section of snake sperm and its length is highly variable, representing from 39% to 70% of total sperm length. Sperm competition also selects for an increase in fibrous sheath area and outer dense fibres 3 and 8, supporting the idea that an increase in the force of the sperm movement is adaptive. Viviparous taxa seem to have lower levels of sperm competition than oviparous taxa, probably because viviparity imposes reproductive constraints on females, which determine the rate of encounters between males and females.